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Wed, 17 Feb 2021 06:00:17 -0800 (PST) MIME-Version: 1.0 References: <20210125153057.3623715-1-balsini@android.com> <20210125153057.3623715-6-balsini@android.com> In-Reply-To: <20210125153057.3623715-6-balsini@android.com> From: Miklos Szeredi Date: Wed, 17 Feb 2021 15:00:06 +0100 Message-ID: Subject: Re: [PATCH RESEND V12 5/8] fuse: Introduce synchronous read and write for passthrough To: Alessio Balsini Cc: Akilesh Kailash , Amir Goldstein , Antonio SJ Musumeci , David Anderson , Giuseppe Scrivano , Jann Horn , Jens Axboe , Martijn Coenen , Palmer Dabbelt , Paul Lawrence , Peng Tao , Stefano Duo , Zimuzo Ezeozue , wuyan , fuse-devel , kernel-team , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Jan 25, 2021 at 4:31 PM Alessio Balsini wrote: > > All the read and write operations performed on fuse_files which have the > passthrough feature enabled are forwarded to the associated lower file > system file via VFS. > > Sending the request directly to the lower file system avoids the > userspace round-trip that, because of possible context switches and > additional operations might reduce the overall performance, especially > in those cases where caching doesn't help, for example in reads at > random offsets. > > Verifying if a fuse_file has a lower file system file associated with > can be done by checking the validity of its passthrough_filp pointer. > This pointer is not NULL only if passthrough has been successfully > enabled via the appropriate ioctl(). > When a read/write operation is requested for a FUSE file with > passthrough enabled, a new equivalent VFS request is generated, which > instead targets the lower file system file. > The VFS layer performs additional checks that allow for safer operations > but may cause the operation to fail if the process accessing the FUSE > file system does not have access to the lower file system. > > This change only implements synchronous requests in passthrough, > returning an error in the case of asynchronous operations, yet covering > the majority of the use cases. > > Signed-off-by: Alessio Balsini > --- > fs/fuse/file.c | 8 ++++-- > fs/fuse/fuse_i.h | 2 ++ > fs/fuse/passthrough.c | 57 +++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 65 insertions(+), 2 deletions(-) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 953f3034c375..cddada1e8bd9 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -1581,7 +1581,9 @@ static ssize_t fuse_file_read_iter(struct kiocb *iocb, struct iov_iter *to) > if (FUSE_IS_DAX(inode)) > return fuse_dax_read_iter(iocb, to); > > - if (!(ff->open_flags & FOPEN_DIRECT_IO)) > + if (ff->passthrough.filp) > + return fuse_passthrough_read_iter(iocb, to); > + else if (!(ff->open_flags & FOPEN_DIRECT_IO)) > return fuse_cache_read_iter(iocb, to); > else > return fuse_direct_read_iter(iocb, to); > @@ -1599,7 +1601,9 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from) > if (FUSE_IS_DAX(inode)) > return fuse_dax_write_iter(iocb, from); > > - if (!(ff->open_flags & FOPEN_DIRECT_IO)) > + if (ff->passthrough.filp) > + return fuse_passthrough_write_iter(iocb, from); > + else if (!(ff->open_flags & FOPEN_DIRECT_IO)) > return fuse_cache_write_iter(iocb, from); > else > return fuse_direct_write_iter(iocb, from); > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index 8d39f5304a11..c4730d893324 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -1239,5 +1239,7 @@ int fuse_passthrough_open(struct fuse_dev *fud, > int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff, > struct fuse_open_out *openarg); > void fuse_passthrough_release(struct fuse_passthrough *passthrough); > +ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *to); > +ssize_t fuse_passthrough_write_iter(struct kiocb *iocb, struct iov_iter *from); > > #endif /* _FS_FUSE_I_H */ > diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c > index cf993e83803e..d949ca07a83b 100644 > --- a/fs/fuse/passthrough.c > +++ b/fs/fuse/passthrough.c > @@ -4,6 +4,63 @@ > > #include > #include > +#include > + > +#define PASSTHROUGH_IOCB_MASK \ > + (IOCB_APPEND | IOCB_DSYNC | IOCB_HIPRI | IOCB_NOWAIT | IOCB_SYNC) > + > +static void fuse_copyattr(struct file *dst_file, struct file *src_file) > +{ > + struct inode *dst = file_inode(dst_file); > + struct inode *src = file_inode(src_file); > + > + i_size_write(dst, i_size_read(src)); > +} Hmm, I see why this is done, yet it's contrary to what's been set out at the beginning: "All the requests other than reads or writes are still handled by the userspace FUSE daemon." Maybe just use fuse_write_update_size() instead of copying the size from the underlying inode. > + > +ssize_t fuse_passthrough_read_iter(struct kiocb *iocb_fuse, > + struct iov_iter *iter) > +{ > + ssize_t ret; > + struct file *fuse_filp = iocb_fuse->ki_filp; > + struct fuse_file *ff = fuse_filp->private_data; > + struct file *passthrough_filp = ff->passthrough.filp; > + > + if (!iov_iter_count(iter)) > + return 0; > + > + ret = vfs_iter_read(passthrough_filp, iter, &iocb_fuse->ki_pos, > + iocb_to_rw_flags(iocb_fuse->ki_flags, > + PASSTHROUGH_IOCB_MASK)); Please split this line up into: rwf = ioctb_to_rw_flags(...); ret = vfs_iter_read(..., rwf); > + > + return ret; > +} > + > +ssize_t fuse_passthrough_write_iter(struct kiocb *iocb_fuse, > + struct iov_iter *iter) > +{ > + ssize_t ret; > + struct file *fuse_filp = iocb_fuse->ki_filp; > + struct fuse_file *ff = fuse_filp->private_data; > + struct inode *fuse_inode = file_inode(fuse_filp); > + struct file *passthrough_filp = ff->passthrough.filp; > + > + if (!iov_iter_count(iter)) > + return 0; > + > + inode_lock(fuse_inode); > + > + file_start_write(passthrough_filp); > + ret = vfs_iter_write(passthrough_filp, iter, &iocb_fuse->ki_pos, > + iocb_to_rw_flags(iocb_fuse->ki_flags, > + PASSTHROUGH_IOCB_MASK)); Same here. Thanks, Miklos